Volume control device



Nov. 22, 1938. J. YoLLEs VOLUME CONTROL DEVICE 3 Sheets-Sheet 1 Filed April 18. 1934 www INVENToR JACOB YOLLES oRNEY 4 Nov. 22, 1938. J. YOLLES 2,137,435

VOLUME CONTROL DEVICE Filed April 18. 1934 3 Sheets-Sheet 2 R mm u @ad w ww W mm A 5 Sheets-Sheet 3 J. YoLLEs VOLUME CONTROL DVICE Filed April 18. 1954 Nov. 22, `1938.

lNvEN'roR JACOB YOLLES A TQRNEY REMPZ.

Patented Nov. 22, 1938h UNITED STATES VOLUME CONTROL DEVICE Jacob Yolles, Bronx, N. Y., assignor to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application April 18, 1934, Serial No. 721,136

10 Claims.

My present invention relates generally to high frequency transmission control devices, and more particularly to a novel and improved type of volume control instrumentality for a radio receiver.

It may be stated that it is one of the prime objects of this invention to provide a device for eiiiciently and smoothly regulating the transmission of high frequency energy between a source of such energy and a load circuit tuned to the frequency of the energy, the-device being so constructed as to have no detuning effect on the tuned load circuit.

Another important object of the invention is to provide a volume control arrangement for a radio receiver, the control being purely capacitative in nature and being capable of employment between the signal collector and the first tuned network, or between the output circuit of a radio frequency amplifier and a following tuned input Circuit; the volume control instrumentality being essentially characterized by its ability to compensate for any detuning eiect it may have upon any associated tuned network.

Another object of the invention involves the provision of a capacitative volume control device for a radio receiver, the control being constructed in such a manner that it includes an element performing the double function of compensating for detuning effects upon the receiver and simultaneously shielding an associated tuned circuit from a preceding high frequency?, input network.

Still another object of the invention is to furnish a volume control unit for a radio receiver, the unit comprising three cylindrical electrodes and one of the electrodes being adapted to be connected to a source of signal energy, such as the plate of an amplifier or an antenna, a second of the electrodes being arranged for connection to the grid of a following tube, and the third electrode being arrangedl for connection across the tuned input vnetwork connected to the following tube, the volume control action being provided by producing relative motion between the grid electrode and the other two electrodes, and the motion being engendered through a manually operable device, or through a device responsive to received signal amplitude 'variations.

And still other objects of the invention are to provide a volume control device of dependable and durable construction, the device being characterized by its ability to vary the signal energy transfer from the signal source to a following tuned network without producing detuning or (Cl. 25o-20) the said network, and these functions being accomplished simply and economically by a unit readily assembled in a radio receiver.

Fig. 1 shows one embodiment of the invention disposed between a pair of signal amplifiers,

Fig. 2 diagrammatically shows the manner of incorporating the present invention, in ganged construction, in the radio frequency amplifier section of a receiver,

Fig. 3 shows, in partial section, a portion of a receiver chassis showing the actual embodiment of the volume control unit of Fig. 1 in the chassis,

Fig. 4 shows a modified form of the invention, illustrated in Fig. 1,

Fig. 5 schematically shows a modification of the ganged embodiment of Fig. 2.

Figs. 6, 7 and 8 each show still further modication of the invention.

Considering these various figures, the volume of a receiver can be regulated in a manner shown in Fig. 1, and in the latter the numerals I and 2 denote a pair of cascaded space discharge tubes of the screen grid type. The control grid of tube I has the input energy, which in this case may be intelligence modulated carrier energy of a super-audible frequency, impressed upon it. rI'he anode of tube 2 may be connected to a demodulator, a frequency changer device or another stage of carrier frequency amplication. In Vother words the tubes I and 2 may be in the tuned radio frequency amplifier section of a radio receiver, and` they may be in the intermediate frequency amplier section of a superheterodyne receiver.

In any case, the network coupling the output electrodes of tube I to the input electrodes of tube 2 comprises the variable capacitor device V. This device consists of a pair of co-axial, spaced metallic sleeves 3 and 4 arranged in alignment on a tube 5 made of insulation material. The latter may be a phenol condensation product or any other well known type of insulation composition. The sleeves- 3 and 4 may be oomposed of any substance commonly used for manufacturing condenser plates, and there may be mentionedaluminum, brass, copper and the like. The sleeves are preferably xedly secured to the exterior of the tube 5, the sleeve 4 being secured to a grounded metallic plate 6.

The plate 6 may be composed of the same materials as the sleeves 3 and 4, and the plate may be soldered to the sleeve 4 to effectively establish the latter at ground potential. The

plate Ii .may assume any desired configuration consistent with the construction of the remainder of the receiver elements and chassis. Its functions are two-fold; it serves as a physical partition between the coil I in the output circuit of the preceding tube and the following resonant network 8, and in this function electromagnetically shields the coil i from network 8. Again, the partition 5 functions as an electrostatic shield between sleeve 3 and the network 8, thus preventing stray capacity coupling between these elements.

Within the interior of tube 5 is disposed a metallic electrode, or plunger, 9. The cross-sectional diameter of the plunger is such that it may be readily reciprocated within the interior bore of tube 5. The plunger may be constructed of the same material as the sleeves 3, 4 and partition 6, and may be hollow or solid. The tube 5 functions as a dielectric between the stator sleeve S and the electrode element 9, and relative displacement between these two electrodes result in a variation of the capacity magnitude of the condenser effectively coupling the high radio frequency potential points of coil 'I and network 8.

The coil 1 has one side thereof connected to the positive terminal of the direct voltage supply source B (not shown), while the high alternating voltage side of the coil is connected to the anode -of tube I and, by a lead I0, to the stator electrode 3 of the adjustable volume condenser V. The usual grid bias networks II', II' are shown in the cathode leads of tubes I and 2 re spectively, and a radio frequency by-pass condenser is shown connected between the low alternating Voltage side of coil T and the ground side of bias network II. The resonant network 8 comprises the usual inductor I2 and shunt variable tuning condenser I3. The low alternating voltage side of network 8 is grounded, while the high side is conductively connected to the electrode 9 through a path including lead I4 and metallic rod I5.

One end of rod I5 is rigidly secured to plunger 9, while the opposite end is provided with a nonconductive manipulating means I6 preferably made of some insulation material. The connection between lead I4 and rod` I5 has been generalized, and it will be understood that the lead 4 may be spirally wound around the rod, as shown in Fig. 2, and soldered thereto. By reciprocating the plunger 9 within tube 5, the intensity level of the wave energy delivered from ampliiier 2 can be regulated.

The coil I is a high impedance inductance having a natural frequency below, but closely adjacent to, the lowest frequency to be transmitted between tubes l and 2. The reference character I'l' designates the distributedcircuit capacity between ground and the plate side of coil l, the capacity being shown in dotted lines, A by-pass condenser I8, of low impedance to currents of wave frequencies, is connected between the ground side of network I I and the low alternating voltage side of coil 'I.

In considering the operation of the present volume control, it is pointed out that the gain in an amplifier of high frequencies can be controlled by varying a direct voltage of an electrode, such as the control grid. Such regulation, it is well known, gives rise to Various undesirable responses in the amplifier output due to nonlinear operation of the amplifier. Gain control may also be had by varying the energy transfer between coupling elements in the amplifier. This method is particularly advantageous in an amplifier of the type shown in Fig. l wherein a high impedance amplifier output coil is employed. The coupling between the primary coil I and the secondary coil I2 is provided through condenser V. When the value of this capacitative coupling is varied, the gain is changed.

The gain control provided by varying a coupling condenser is not only free from the bias method objections, but is mechanically desirable. However, it will be observed that a detuning effect is intr-oduced into network 8. This arises because of the following reasons: the capacitative coupling required with commercial broadcast receiver circuits for optimum gain is on the order of 5 to 2O mmfds. The capacity effectively across the tuned secondary I2 comprises in part this variable coupling capacity. The tuned circuit 8 is therefore detuned as the condenser V is varied. This is not only true of inter-stage coupling networks, but also holds for the antenna circuit. The volume control condenser V is connected, in Fig. 1, between the high alternating voltage point on the tuned network 8 and ground, the return to ground being made through the high impedance primary, the self-capacity of the latter and the capacity within the tube, or the antenna if there disposed. The dotted line capacity I'I represents the return path to ground.

The construction of the control device V is such that it compensates for the detuning of the associated tuned circuit. As the magnitude of the coupling capacity is decreased, an equal increment of capacity is added to the tuned circuit. The reverse is, of course, true when the magnitude is increased. The movement of the plunger 9 vinto concentric relation with sleeve 3 results in a decrease of the capacity between plunger 9 and sleeve 4. As the plunger moves to the left the volume of the amplifier output increases and the compensating capacity across tuned network 8 decreases. When the plunger moves to the right the volume decreases, but the compensation capacity increases.

Therefore it will be seen that as the value of the coupling capacity is varied, there is produced a simultaneous variation of capacity across the tuned circuit 8 in a sense to compensate for any detuning effect. The total effective capacity across the resonant network 8 is a constant. regardless of the position of plunger 9; assuming, of course, the variable tuning condenser I3 is not adjusted. The dual function of the member B will now be appreciated. It not only serves to ground sleeve 4 for detuning compensation. but it serves as a magnetic and electrostatic shield between coil 1 and sleeve 3 respectively and network 8.

The lead 'I need not be connected to the high alternating voltage side of network 8. The lead can be connected, for example, to an intermediate point on coil I2. Further, it will be understood that the device V may be disposed between the antenna circuit and the first amplifier tube, as shown in the first stage of the system shown in Fig. 2. Again, it will be clear that the condenser I3 may be a fixed one, as in an intermediate frequency amplifier stage, and the volume control device used in the same manner.

Since the sleeve 4` is grounded through the partition 6 it follows that the variation of capacity between plunger 9 and sleeve 4, for axial displacements of the plunger, follows the simple law for co-axial cylinders. 'I'he variation of capacity between the stator 3 and electrode 9 departs from this law. This is due to the fact that the sleeve 3 is not directly grounded, but is connected to ground through the series impedance path described above. In some cases it becomes desirable to compensate for this effect; in such instances I have discovered that designing the sleeve 4 to have a length about two thirds that of sleeve 3 provides suilicient compensation.

The relative lengths of sleeves 3 and 4 depend, in general, upon the type of coil used at 1, the type of tubes employed and upon the circuit residual capacity. Special volume control variation laws may be secured by shaping the electrodes of the device V in a predetermined manner. Thus, in Fig. 4 is shown one such predetermined geometric relation between tubes 3, 4. The tubes, instead of being cylinders, are sections thereof. Those skilled in the art will readily be ableto design other geometric con gurations for the electrodes 3, 4 and 9 to secure desired capacity variation relations.

In Fig. 2 is shown in schematic manner a unicontrolled'gang of volume control units, each constructed as shown in Fig. l, embodied in a receiver. Only elements of the system in Fig. 2 are shown which are essential to a clear understanding of the invention. Thus the numeral I9 represents the chassis, or ground element, of the receiver. The signal source, an antenna 20 in this case, is connected between the sleeve 2|, of the first volume control unit V1, and ground. The antenna includes a high impedance coil 21, and the plunger electrode 29 is connected to the first tuned network 28.

The detuning compensation electrode 24 is soldered to the shield 26. The latter is conductive` ly secured to the chassis |9, and hence is established at ground potential. It will be understood that the partition 26 is common to all the units Vi-Vz-Vs. The partition 26 is disposed between the tuned networks 2B, 28', 28" as one group and the coils 21, 21', 21" as another group. The three sleeves 24, 24' and 24" are soldered to the common shield 26 adjacent corresponding spaced insulation tubes 25, 25' and 25". Each tube carries, as shown, a sleeve 2|, and therefore the stators 2|, 2| and 2|" are electrostatically shielded from the tuned networks 28, 28 and 28", disposed on the opposite side of the partition 26.

The receiving system shown in Fig. 2 comprises amplifier tubes 30 and 3|, the signal grid of tube 3U being connected to the high alternating voltage side of network 28. The plunger 29 is connected to the same side of network 28, a rod 32 being secured to the plunger to permit reciprocation of the latter through tube 25. Similarly, the signal grid of tube 3|, and the plunger 29', are connected to the high alternating voltage side of network 28'; a rod 33 being connected to the plunger 29'. The plunger 29" is connected to the tuned network 28, and the latter may be coupled to a rectifier, such as a demodulator. The latter may then be followed by the usual audio amplifier and reproducer.

Each tuned network includes a Variable tuning condenser, conventionally shown, and the mobile electrodes of the tuning condensers can be arranged for uni-control as is well known. The anode of tube 30 is connected by lead 3l|A to stator 2| and one side of coil 21', the opposite side thereof being connected to the positive terminal of the anode direct voltage supply source; a radio frequency by pass condenser connecting the latter side of coil 21' to ground.` In the same manner the anode of tube 3| is connected by lead 34' to rcoil 21", the latter being connected to ground, through condenser 35', and also to the positive terminal of the anode voltage supply sourcev The lead 34 is connected to sleeve 2|.

The cathode and screen grid electrodes of each of tubes 30, 3| have been omitted to simplify the drawings. However, it will be clearly understood that these electrodes, as well as any additional ones, may be employed in the manner shown in Fig. 1. The anode leads 34 and 311' are shown enclosed in grounded shielding sheaths, 36 and 36 respectively, up to the partition 26. A common mechanical drive means is employed for rods 32, 33, 33. This means comprises a cross bar 31 having a rack 38 xedly secured thereto. A manipulating knob 39, secured to a pinion 4B in mesh with the rack teeth, provides means for adjusting the positions of the plungers. The ends of rods 32, 33 and 33' are threaded into threaded bores in the bar 31. Nuts 4| secure the threaded ends of the rods to the bar 31, and thus the initial positions of the plungers may be adjusted. That is to say, the relative motion, or initial setu tings, of the individual pl'ungers may be prese'- lected so that no tube is overloaded at any time. A certain value of antenna signal voltage being assumed, the minimum setting of the plunger 29 is chosen so that the tube 3D will not be overloaded by swinging the signal grid to a point on the tube characteristic beyond the linear region. The initial positions of plungers 29' and 29" are then selected to prevent overloading of tube 3| and the rectifier tube at maximum volume setting. Of course, the initial positions of the three plungers can be adjusted to be the same or overlapping.

It was explained in connection with Fig. l that the coil 1 could be naturally resonant to a frequency below, but not greatly below, the lowest frequency to be received. For an arrangement of the type shown in Fig. 2, it is desirable to use slightly differing values of natural frequencies for coils '21, 21' and 21". For example, such values couldhe y539,* 520 and 5l() kilocycles respectively for the three coils.

In general, the different input coilsv in each stage should differ from each other by a small, predetermined value of natural frequency, and all the frequencies should be below the lowest frequency to be received. If all the input coils were of the same frequency then the system might build up appreciable gain at one frequency, the natural frequency of the coil circuits, and cause instability, noise and'response to code interference.

' In Fig. 3 there is shown a portion of the chassis of the receiving system in Fig. 2. 'I'he elements shown are those between tube 3U and the tunable network 28'. The metallic base plate 42 has mounted upon it the tube 3G, the shielding can 43 housing the coil of the tunable network 28. The numeral 44 designates the gang condenser, the capacity due to the tuning condenser across the coil of network vlifi'is shown in dotted lines. The shielding partition 26 is secured to the bottom face of plate 42, and thus is grounded. The remaining elements need not be described, since their reference numerals are similar to those used in connection with the same elements in Fig. 2.

In Fig. 5 there is shown a modified construction of the ganged volume control unit used in Fig. 2. The diierence between the two constructions resides in the manner of securing the overlapping relation between the plungers in Fig. 5. For this reason reference numerals are applied solely to those elements of Fig. 5 which are not found in Fig. 2. The three plunger rods are secured to racks 50, 5| and 52 respectively. The pinions 50', 5| and 52 mesh with racks 50, 5| and 52 respectively, and the manipulating shaft 53 couples the three pinions. The latter are designed to have different numbers of teeth. The driving pinions, or the racks, are designed to drive the plungers at different speeds. Of Course, the representation in Fig. 5 is purely schematic, and those skilled in the art will understand that obvious mechanical devices can be used to render the construction mechanically perfect.

Fig. 6 shows a modification of the mechanical drive means for a volume control unit plunger. In this form of the device the electrode elements of the volume control unit V are the same as in Fig. 1. The plunger 9 is secured, in this embodiment, to one end of a connecting tube 60 provided with a bore BI. A bolt 62, threadedly engaged with the bore 62, secures the plunger 9 in place. A second bolt B3, also threadedly engaged with the bore B2, secures the tube S to a link E4 provided at one end with a pin 65. The latter is arranged to reciprocate along a slot 6G provided in toggle member B1. The sha-ft 88, carrying the manipulating knob (not shown), is affixed to member 61. Of course, a plurality of plungers can be mechanically coupled to a link member 64, and in such case adjustment of shaft 68 results in movement of the plungers toward, or away from, the electrodes 3 depending upon the direction of adjustment of shaft 68.

Another modification of the mechanical drive for the plunger 9 is shown in Fig. 7; in this embodiment a flexible cord, or cable, 10 is used to adjust the position of plunger 9 with respect to 4l()` electrodes 4 and 3. In this case, as in the other embodiments, the numeral denotes the dielectric tube through Whose bore the plunger 9 reciprocates. The partition 5 is extended to proviole a guide tube 1| for a guide rod 12. The latter has one end thereof rigidly affixed to a drawn bar 13, the latter being made of an insulation material, such as a phenol condensation product. The opposite end of rod 12 is bolted to a washer 14, a compression spring 15 being disposed between the washer 14 and an additional washer 14.

The bar 13 is provided with a hook 15 to which is secured one end of the cable 10. The opposite end of the cable is secured to the drive pulley 16,

'. an idler pulley 11 guiding the cable towards the pulley 18. An operating knob 18 is rigidly aflixed to pulley 16, rotation of the knob in clockwise direction resulting in movement of the bar 13 to the left. The plunger 9 is mechanically coupled to the draw bar 13 by securing it to one end of a soa-ghetti tube 19.

The opposite end of the tube 19 is rigidly affixed to bar 13. The lead 80, which is connected between the plunger 9 and the grid of the following tube, has one end thereof secured to the base of the said mobile electrode, it being pointed out that the interior of the mobile electrode is hollow. The lead is disposed within the bore of tube 19, and the latter therefore performs the double function of housing the grid lead 80, and coupling the electrode 9 to draw bar 13.

It will now be seen that clockwise rotation of knob 18 results in adjustment of electrode 8 toward electrode 4. With the electrode 9 in the position shown in Fig. '1 the spring 15 is compressed. As the knob is moved counter-clockwise the spring 15 pulls the bar 13 towards partition 6. Of course, suiilcient frictional engagement is provided between knob 18 and panel 80', or between pulley 16 and panel 80', to prevent spring 15 from forcing bar 13 away from a desired adjusted position. Any mechanical expedient, well known to those skilled in the art, may be employed to supply the requisite force to neutralize the push of spring 15 at any position of knob 18.

In Fig. 8 is shown still another modification of the invention, the mobile electrode 8| in this case being connected to the plate of the preceding tube and the stator electrode 82 being connected to the following tuned circuit 83. The detuning compensation electrode 84 is movable with the electrode 8| in this embodiment, and the mobile electrode 8| is rendered mobile in response to variations in received signal amplitude. The circuit elements of the receiving system are shown in conventional form, and it will be understood that the numeral 85 denotes a stage such as that including tube in Fig. 1. The numeral 86 designates a following stage constructed as shown in Fig. l. The dielectric tube 81 is similar to the tube 5 in Fig. 1, and the electrode 8| may be secured between adjacent sections 88 and S8 of an adjusting shaft.

The shaft sections are made of an insulation material, such as a phenol condensation product. The electrodes 8|, 82 and 84 may be made of brass, and it will be understood that the electrode 84 is aixed at 84 to shaft section 88. The electrode 84 is concentric with electrodes 8| and 82, the grounded lead 89 establishing the electrode 84 at ground potential. The section 88 is provided with a magnetic solenoid armature |00, and a compression spring |0| is disposed between the free end of the armature and a fixed surface |02. A solenoid winding |03 is arranged about the armature |08, and the leads |04 of the winding are connected to the plate circuit of detector |05.

rIhe connections to the detector plate circuit are so well known to those skilled in the art that they need not be shown. The detector may be of the biased type, and in that case an increase in signal amplitude will result in a corresponding increase in detector plate current.

This will increase the intensity of the magnetic field tending to draw armature |00 into the winding |03. The electrodes 8| and 84 are thereby drawn towards the solenoid winding |03. Thus, it will be seen that as the signal amplitude increases, the transfer of signal energy from stage 85 to stage 85 is decreased; the effective capacity in tuned circuit 83, however, is constant due to the electrode 84.

If the signal amplitude decreases the solenoid magnetic held intensity decreases. and the expanding spring |0| pushes the armature |00 toward the electrode 82. crease in the capacity between electrodes 8| and 82. thereby increasing the signal energy transfer between stages 85 and 86. Simultaneously, the compensation capacity between electrode 84 and electrode 82 decreases, and the tuning of network 83 remains undisturbed.

The net result of the automatic adjustment of electrodes 8| and 84 is to maintain the amplitude level of signal energy fed to the detector |05 substantially constant, this being accomplished by varying the signal transfer between stages through a variable coupling capacity. De-

This.l results in an in` tuning effects are compensated for by simultaneously adjusting the effective. capacity in tuned circuits in a sense to maintain the effective capacity constant.

It will be evident that .an additional set of volume control electrodes 8|, 82 and 84 may be associated with shaft section 88 for control between the antenna and stage 85, and another set of electrodes may be associated with shaft section 8f3 for control between the stage 86 and detector H15. Such three sets of volume control electrodes would then be operated by the armature IUD, and in accordance with variations in the detector plate current. The construction of such a gang of controls need not be shown in detail since each of the sets of electrodes would be an exact duplicate of that shown in Fig. 8. Again, the three control units may be' overlapping in action as explained in connection with Fig. 5. Further, it will be understood that, in place of the detector, a special rectifier may be employed, the rectifier having impressed upon it a portion of the signal energy fed to the detector 35. The volume control rectiiier output would feed the winding H33. Finally, stages 85 and St may be the intermediate frequency amplifier stages of a superheterodyne receiver.

What I claim isz- 1. In a radio receiver, a tube provided with an input network tuned to an operating frequency, a source of signal carrier energy including an impedance, a variable capacitor coupling said impedance to the tuned network, the capacitor including a first electrode connected to the impedance, a second electrode connected to a point of low signal voltage on the tuned network, the connection to said point comprising a conductive means electrically shielding the said impedance from the said tuned input network, and a third eiectrode connected to a point on the network of relatively higher signal voltage, means' responsive to carrier energy amplitude variations for producing relative motion between the third electrode and the `first two electrodes.

2. In a radio receiver, a tube provided with an input network tuned to an operating frequency, a source of signal carrier energy including an impedance, a variable capacitor coupling said impedance to the tuned network, the capacitor including a rst electrode connected to the impedance, a second electrode connected to a point of low signal voltage on the tuned network, and a third electrode connected to a point on the network of relatively higher signal voltage, means responsive to variations in the amplitude of the carrier energy for producing relative motion between the third electrode and the first twoelectrodes, the said impedance being a coil naturally resonant to a frequency below the lowest frequency to be received, the second electrode cooperating with the third electrode to compensate for detuning of the tuned network when the capacity between the first and third electrodes is varied, the connection from the second electrode to said first point including a metallic plate to shield the first electrode and coil from the tuned network.

3. In a radio receiver provided with a plurality of cascaded amplifier tube stages, each stage comprising a tube having a tuned input circuit coupled to a coil in the plate circuit of the next preceding tube, and a volume control device comprising a plurality of adjustable coupling condensers, each condenser consisting of a fixed electrode connected to one of the preceding plate coils, a mobile electrode connected to the grid of the following tube and a detuning compensation electrode connected to the cathode side of the following tuned circuit, and a common means for adjusting the mobile electrodes of all the condensers at different rates.

4. In a radio receiver provided with a plurality of cascaded amplier tube stages, each stage comprising a tube having a tuned input circuit coupled to a coil in the plate circuit of the next preceding tube, and a volume control device comprising a plurality of adjustable coupling condensers, each condenser consisting of a xed electrode connected to one of the preceding plate coils, a mobile electrode connected to the grid of the following tube and a detuning compensation electrode connected to the cathode side of the following tuned circuit, and a common means for adjusting the mobile electrodes of all the condensers, the connection from each compensation electrode including means electrically shielding a preceding plate coil from the following tuned network.

5. In a radio receiver provided with a plurality of cascaded amplifier tube stages, each stage comprising a tube having a tuned input circuit coupled to a coil in the plate circuit of the next preceding tube, and a volume control device including at least one adjustable coupling condenser, said condenser comprising a xed electrode connected to one of the preceding plate coils, a mobile electrode connected to the grid of the following tube and a detuning compensation electrode connected to the cathode side of the following tuned circuit, means for adjusting the mobile electrode of the condenser, said means being responsive to received signal amplitude variations.

6. A radio receiver including a signal collector, an amplifier having a tuned input circuit, a variable condenser coupling the collector to the input circuit, the condenser including means for cornpensating for detuning of the input circuit when the condenser is varied, and means, responsive to received signal amplitude variations, for regulating the coupling condenser.

7. In radio receiving apparatus, a signal carrier energy exciting circuit, a utilizing circuit, one of said circuits being tuned to the frequency of the desired signal carrier energy, means comprising a variable coupling between said two circuits, means responsive to amplitude variations of the signal carrier energy for varying said coupling and means for maintaining said tuning substantially independent of changes in said coupling.

8. In a radio receiving system, a signal carrier energy exciting circuit, a signal energy utilizing circuit, one of said circuits being tuned to said carrier energy means comprising a variable capacity for coupling said two circuits, means for maintaining said tuning substantially independent of variations in said capacity, and means responsive to amplitude variations of the signal carrier energy for varying said coupling.

9. In signalling apparatus, a primary circuit including a source of signal energy, an amplifier having a tuned input circuit, a variable condenser coupling the primary circuit to the input circuit, the condenser including means for compensating for detuning of the input circuit when the condenser is varied and means responsive to amplitude variations in the signal energy from said source for regulating the coupling condenser.

10. In a radio receiver, a primary circuit including a signal collector, an ampliiier having an input circuit tunable over a range of frequencies, a variable condenser coupling the primary circuit to the input circuit, said condenser including means for compensating for detuning of the input circuit when the condenser is varied and means responsive to received signal amplitude -variations for regulating the coupling condenser to thereby provide coupling between the primary circuit and said input circuit which varies inversely proportional to the strength of the received signal energy.

JACOB YOLLES. 

